Generally, attempts to improve the fuel efficiency of construction machines have been made. In particular, as the importance of fuel efficiency increases, attempts to decrease an engine RPM when a construction machine is not used have been continuously made.
Meanwhile, an increase in the convenience of a user is required. For the convenience of a user, for example, an air conditioner is used, and other electric devices, etc. may be used. The other electric devices including the air conditioner consume electrical energy. Electrical energy is generated by operating an alternator by means of the power of an engine.
In other words, although an engine RPM needs to be decreased when fuel efficiency is taken into account, the engine RPM needs to be maintained at a predetermined level or higher in order to maintain the convenience of a user. Therefore, in order to optimally control the engine RPM, there is a demand for an advanced control technology for a construction machine.